1. ADAP deficiency impairs megakaryocyte polarization with ectopic proplatelet release and causes microthrombocytopenia
- Author
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Markus Bender, Markus Spindler, David Stegner, Paquita Nurden, Yvonne Schurr, Judith M.M. van Eeuwijk, Annegret Reinhold, and Bernhard Nieswandt
- Subjects
Blood Platelets ,0301 basic medicine ,Podosome ,Platelet disorder ,Immunology ,Biochemistry ,Thrombopoiesis ,Extracellular matrix ,Mice ,03 medical and health sciences ,Species Specificity ,Megakaryocyte ,Bone Marrow ,Cell-Derived Microparticles ,medicine ,Animals ,Platelet ,Platelet activation ,Cell Shape ,Cellular Senescence ,Cytoskeleton ,Adaptor Proteins, Signal Transducing ,Cell Size ,Mice, Knockout ,Platelet Count ,Chemistry ,Cell Membrane ,Cell Biology ,Hematology ,Platelet Activation ,Thrombocytopenia ,Cell biology ,030104 developmental biology ,medicine.anatomical_structure ,Podosomes ,Splenectomy ,Bone marrow ,Megakaryocytes - Abstract
Bone marrow (BM) megakaryocytes (MKs) produce platelets by extending proplatelets into sinusoidal blood vessels. Defects in thrombopoiesis can lead to thrombocytopenia associated with increased bleeding tendency. Recently, the platelet disorder congenital autosomal-recessive small-platelet thrombocytopenia (CARST) was described; it is caused by mutations in the adhesion and degranulation-promoting adaptor protein (ADAP; synonym: FYB, SLAP130/120) gene, and characterized by microthrombocytopenia and bleeding symptoms. In this study, we used constitutive ADAP-deficient mice (Adap-/- ) as a model to investigate mechanisms underlying the microthrombocytopenia in CARST. We show that Adap-/- mice display several characteristics of human CARST, with moderate thrombocytopenia and smaller-sized platelets. Adap-/- platelets had a shorter life span than control platelets, and macrophage depletion, but not splenectomy, increased platelet counts in mutant mice to control levels. Whole-sternum 3-dimensional confocal imaging and intravital 2-photon microscopy revealed altered morphology of ADAP-deficient MKs with signs of fragmentation and ectopic release of (pro)platelet-like particles into the BM compartment. In addition, cultured BM-derived MKs lacking ADAP showed reduced spreading on extracellular matrix proteins as well as activation of β1 integrins, impaired podosome formation, and displayed defective polarization of the demarcation membrane system in vitro. MK-/platelet-specific ADAP-deficient mice (PF4-cre) also produced fewer and smaller-sized platelets and released platelets ectopically. These data demonstrate that the abnormal platelet production in the mutant mice is an MK-intrinsic defect. Taken together, these results point to an as-yet-unidentified role of ADAP in the process of MK polarization and platelet biogenesis.
- Published
- 2018